The invention pertains to methods of making magnetoresistive memory devices, such as, for example, magnetic random access memory (MRAM) devices.
Numerous types of digital memories are utilized in computer system components, digital processing systems, and other applications for storing and retrieving data. MRAM is a type of digital memory in which digital bits of information comprise alternative states of magnetization of magnetic materials in memory cells. The magnetic materials can be thin ferromagnetic films. Information can be stored and retrieved from the memory devices by inductive sensing to determine a magnetization state of the devices, or by magnetoresistive sensing of the magnetization states of the memory devices. It is noted that the term xe2x80x9cmagnetoresistive devicexe2x80x9d characterizes the device and not the access method, and accordingly a magnetoresistive device can be accessed by, for example, either inductive sensing or magnetoresistive sensing methodologies.
A significant amount of research is currently being invested in magnetic digital memories, such as, for example, MRAMs, because such memories are seen to have significant potential advantages relative to the dynamic random access memory (DRAM) components and static random access memory (SRAM) components that are presently in widespread use. For instance, a problem with DRAM is that it relies on power storage within capacitors. Such capacitors leak energy, and must be refreshed at approximately 15 nanosecond intervals. The constant refreshing of DRAM devices can drain energy from batteries utilized to power the devices, and can lead to problems with lost data since information stored in the DRAM devices is lost when power to the devices is shut down.
SRAM devices can avoid some of the problems associated with DRAM devices, in that SRAM devices do not require constant refreshing. Further, SRAM devices are typically faster than DRAM devices. However, SRAM devices take up more semiconductor real estate than do DRAM devices. As continuing efforts are made to increase the density of memory devices, semiconductor real estate becomes increasingly valuable. Accordingly, SRAM technologies are difficult to incorporate as standard memory devices in memory arrays.
MRAM devices have the potential to alleviate the problems associated with DRAM devices and SRAM devices. Specifically, MRAM devices do not require constant refreshing, but instead store data in stable magnetic states. Further, the data stored in MRAM devices can potentially remain within the devices even if power to the devices is shutdown or lost. Additionally, MRAM devices can potentially be formed to utilize less than or equal to the amount of semiconductor real estate associated with DRAM devices, and can accordingly potentially be more economical to incorporate into large memory arrays than are SRAM devices.
Although MRAM devices have potential to be utilized as digital memory devices, they are currently not widely utilized. Several problems associated with MRAM technologies remain to be addressed.
Exemplary problems associated with prior art processing are described with reference to FIGS. 1 and 2. FIG. 1 illustrates a wafer fragment 10 comprising a semiconductor substrate 12. To aid in interpretation of the claims that follow, the terms xe2x80x9csemiconductive substratexe2x80x9d and xe2x80x9csemiconductor substratexe2x80x9d are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
A stack 14 is provided over substrate 12, and will ultimately be utilized to form an MRAM device. Stack 14 comprises a conductive material 16, a first barrier layer 18, a first magnetic material 20, a non-magnetic material 22, a second magnetic material 24, and a second barrier layer 26. It is noted that the shown layers are those pertinent to the present invention, and that the layers can be formed physically against one another as shown, or other layers (not shown) can be provided between various of the shown layers in forming an MRAM construction.
Conductive material 16 can comprise, for example, either elemental copper or copper alloys.
Layers 18 and 26 are referred to as barrier layers to indicate that layers 18 and 26 can impede diffusional exchange of materials across the layers. Layers 18 and 26 can alternatively be referred to as spacer layers, or as anti-magnetic layers. Layers 18 and 26 can comprise, for example, elemental tantalum or tantalum nitride (TaN). Layers 18 and 26 can comprise other components in addition to, or alternatively to, tantalum-containing components, such as, for example, Ti, W, TiN, SiN, or SiO2. Layers 18 and 26 can comprise the same compositions as one another, or different compositions.
Magnetic layers 20 and 24 can comprise, for example, one or more of nickel, iron, cobalt, iridium, platinum, ruthenium, and manganese. Layers 20 and 24 can comprise the same compositions as one another, or different compositions. After layers 20 and 24 are incorporated into an MRAM device, one of the magnetic layers 20 and 24 will typically be referred to as a sense layer and the other will be referred to as a reference or pinned layer. Another magnetic layer (not shown) can be provided proximate the reference layer to pin the layer into a particular magnetic orientation.
Non-magnetic layer 22 can comprise either an electrically conductive material (for example, in applications in which the resultant MRAM is to be a giant magnetoresistive (GMR) device), or alternatively can comprise electrically insulative material (for example, in applications in which a resulting MRAM device is to be a tunnel magnetoresistive (TMR) device). Exemplary conductive materials which can be utilized for non-magnetic layer 22 are copper and copper alloys; and exemplary insulative materials which can be utilized for non-magnetic layer 22 are aluminum oxide (Al2O3), silicon oxynitride (SixNyOz, wherein x, y and z are greater than 0) and silicon dioxide (SiO2).
A masking block 30 is shown formed over stack 14. Masking block 30 can comprise photoresist, and can be formed utilizing photolithographic patterning methodologies. Block 30 can further comprise a so-called hard mask alternatively to, or in addition to, a photoresist block. The block 30 is in a shape comprising a desired peripheral pattern. The peripheral pattern is defined by the location of sidewall peripheries 32 and 34 of the masking block.
Referring to FIG. 2, the peripheral pattern of block 30 is transferred to underlying layers 18, 20, 22, 24 and 26 with a suitable etch to extend the peripheral pattern of block 30 through layers 18, 20, 22, 24 and 26. The etched layers 18, 20, 22, 24 and 26 define an MRAM construction 50. The etch utilized for etching through layers 18, 20, 22, 24 and 26 can comprise a primarily physical etch (as opposed to a primarily chemical etching process), such as, for example, ion milling or some of the reactive ion etching processes.
The etching of layers 18, 20, 22, 24 and 26 forms sputtered material 40 as a reaction by-product, and some of the sputtered material deposits on sidewalls of the patterned layers. Sputtered material 40 comprises magnetic components from layers 20 and 24, and accordingly can magnetically interconnect layers 20 and 24 across an outer sidewall of non-magnetic layer 22. Such magnetic interconnection of layers 20 and 24 can render a resultant MRAM device comprising layers 20 and 24 inoperative. Specifically, it is desired that layers 20 and 24 be isolated from one another during operation of an MRAM device. As indicated above, one of magnetic layers 20 and 24 will typically be referred to as a sense layer, and the other of the layers will be referred to as a reference or pinned layer. In operation, information is stored in an MRAM device as a magnetic orientation within layer 24 relative to the magnetic orientation within layer 20. Specifically, if layer 24 has an antiparallel magnetic orientation relative to layer 20, such would correspond to a first memory state, and if layer 24 has a parallel magnetic orientation relative to layer 20 such corresponds to a second memory state. If, however, magnetic layer 24 is magnetically connected to layer 20 through magnetic materials across the sidewall of layer 22, magnetic information from layer 24 can propagate to magnetic layer 20, and vice versa; rendering it difficult, or even impossible, to store information in a device comprising layers 20 and 24.
Another problem associated with the MRAM device 50 of FIG. 2 can be that the layers 18, 20 and 22 are patterned into a same configuration as the layers 24 and 26. In particular applications, it can be desired to have layers 24 and 26 patterned into a different configuration than layers 18, 20 and 22.
It would be desirable to develop new methods for forming MRAM devices which overcome some or all of the above-discussed problems.
In one aspect, the invention encompasses a method of forming a magnetoresistive device. A construction is formed which includes a first magnetic layer, a non-magnetic layer over the first magnetic layer, and a second magnetic layer over the non-magnetic layer. A first pattern is extended through the second magnetic layer and to the non-magnetic layer with an etch selective for the material of the second magnetic layer relative to the material of the non-magnetic layer. A dielectric material is formed over the patterned second magnetic layer, and subsequently a second etch is utilized to extend a second pattern through the non-magnetic layer and at least partway into the first magnetic layer.
In another aspect, the invention encompasses a method wherein a stack comprising a first magnetic layer, a second magnetic layer, and a non-magnetic layer is formed. The non-magnetic layer is between the first and second magnetic layers. A patterned mask is formed over the second magnetic layer, and defines a first pattern. The first pattern is extended into the second magnetic layer, but not entirely through the second magnetic layer, with a first etch. A second etch is then utilized to extend the first pattern entirely through the second magnetic layer and to the non-magnetic layer. The second etch is selective for the material of the second magnetic layer relative to the material of the non-magnetic layer. A dielectric material is formed over the patterned second magnetic layer, and subsequently a third etching process is utilized to extend a second pattern through the non-magnetic layer and first magnetic layer.